A temperature compensated crystal oscillator utilizes a piezoelectric effect of a crystal element to generate a specific frequency. For example, there is proposed a temperature compensated crystal oscillator which is provided with a package which has a substrate, a first frame which is provided on an upper surface of the substrate for providing a first concave portion and a second frame which is provided on a lower surface of the substrate for providing a second concave portion; a crystal element which is mounted on electrode pads which are provided on the upper surface of the substrate; and an integrated circuit element which is provided on the lower surface of the substrate and has a temperature sensor (see for example the following Patent Literature 1).